The present invention relates to leak detection, and more particularly to a passive fluid leak detector and indicator which is particularly suited for detecting leaks in hidden, visually obstructed locations.
Many hydraulic systems have several joints and/or fittings which are not readily visible, and are thus difficult to inspect during normal maintenance. Sometimes minor leakage at such joints is not a problem, so routine inspections are not necessary. With other equipment, such as aerospace systems like the Space Shuttle, leakage can be even more critical than on conventional aircraft or ground hydraulic systems. Maintenance and turn-around inspection times in such specialized craft are therefore impacted by the necessity to verify the hydraulic system integrity. In such cases, hidden joints and fittings can considerably increase this inspection time.
Many so-called "hidden" joints, while not directly accessible visually, can still be easily inspected, for example with inspection mirrors. However, when portions of the hydraulic system are insulated, as in spacecraft such as the Shuttle, such indirect observation is precluded and leak detection becomes a difficult, time consuming, and critical problem. (The Shuttle has over 2,000 joints which must be inspected at the conclusion of each flight.)
The prior art, of course, includes various known means for remote detection of leaks. Much of this technology, however, is elaborate and heavy, and not readily adaptable to use with aerospace systems. There are a number of relatively simple leakage detectors known, but these primarily reveal or provide a telltale at the location of the leak, and are not adequate to provide a remote indication in the environment just described. For example, U.S. Pat. Nos. 2,601,840 (M. F. Smith et al., issued July 1, 1952) and 2,708,896 (M. F. Smith et al., issued May 24, 1955) disclose protective covers for pipe flanges and valves. The covers, which are intended to contain possibly harmful leakage materials, have indicating chemicals to reveal such a leak. In several embodiments a wick may be used to conduct the fluid to an indicator outside the cover by means of capillary action. Remote indication as discussed above, however, is not addressed.
U.S. Pat. No. 3,485,085 (W. M. Hawkins, Jr., issued Dec. 23, 1969) discloses a leak detector around a joint, wherein moisture which leaks condenses and then travels by capillary action to a leak detecting tape. The color and resistivity of the tape then change to reveal the detected leak. The leak detecting tape is displaced a short distance from the joint not due to visual inaccessibility, but to provide room for intervening insulation to keep the leak detecting tape cooler than the joint.
U.S. Pat. Nos. 2,918,033 (Snyder, issued Dec. 22, 1959) and 2,918,893 (Norton, issued Dec. 29, 1959) provide in situ detection of leakage at joints which are apparently already visibly accessible.
U.S. Pat. No. 2,460,215 (K. J. Chase, issued Jan. 25, 1949) discloses a telltale for frozen food packages. A water capsule breaks upon freezing, and subsequent melting causes a wick to convey the water to a visual color changing indicator at the surface of the package being monitored. The device is thus not directed to remote leakage detection. Also, it depends upon a chemical which changes color when wetted by the moisture which is being detected.
As may be seen, therefore, a need still remains for an improved, inexpensive, uncomplicated, and light weight fluid leak indicator for detecting fluid leaks in hidden, visually inaccessible locations. Such an indicator should be easy to install, should preferably be able to provide an indication at a point distant from the leak, and should also be able to readily indicate the presence of leaks without requiring a chemical change in the indicator. Ideally, such an indicator should also be resistant to "false alarms" which might occur from exposure to fluid at locations other than that being monitored. Further, such an indicator should, in the preferred embodiment, be physically self-sustaining, as may be required, such that it can retain its own shape in whatever configuration may be desired.